import pandas as pd
df =pd.DataFrame({'商品':['苹果','香蕉','梨'],
                  '单价(元)':[5,5,4],
                  '销量(kg)':[100,None,None],
                  '库存(kg)':[50,None,70]
                  })
print('原始数据:\n',df)
print('检查缺失值:\n',df.isnull)
print('检查非缺失值:\n',df.notnull)
print('统计每列缺失值的个数:\n',df.isnull().sum())